A wide variety of soap bar compositions and manufacturing processes are known in the art. Commonly, soap bar compositions for toiletry purposes are milled soaps of low moisture content (from about 5% to about 18% water) based on a mixture of tallow and coconut oil feedstocks. Bars having milled soap characteristics can also be prepared from soap of a high moisture content, as described for example in US-A-2,686,761 and US-A-2,970,116 by mechanically working the soap at a temperature of from about 80.degree. F. to 125.degree. F. and by using an appropriate fat feedstock. Such a process has two main advantages; firstly, it is relatively energy-efficient in that less drying of the neat-kettle soap is required; and secondly, it produces soap bars having desirable translucency or transparency as a result of beta-phase soap formation.
From the consumer acceptance viewpoint, of course, the lathering and mildness characteristics of a toilet bar composition are highly important and there is a continuing need to improve these areas of performance. Traditionally, lather enhancement has been achieved in two ways. Firstly, shorter chain fatty acid soaps such as coconut soaps are known to produce a much richer lather than longer chain fatty acid soaps such as those based on tallow and it is therefore common practice in toilet bar manufacture to add up to 50% coconut soap to the tallow fat feedstock. Secondly, superfatting agents such as coconut fatty acid also improve the volume and richness of the lather when added to toilet bars in levels of up to about 10%. At higher levels, however, coconut soaps increasingly have a detrimental effect on bar mildness while fatty acids can produce undesirable softening of the bar. Moreover, coconut soaps and fatty acids are both expensive commodities and it would therefore be desirable to achieve improvements in lathering without recourse to high levels of these ingredients.
In the case of beta-phase soaps, moreover, there is a more fundamental difficulty in achieving high lathering. Fat feedstocks which are relatively rich in shorter chain (less than 16 carbon atoms) saturated fatty acids inhibit the formation of beta-phase soap and are therefore unsuitable for making transparent or translucent soap bars. In a similar way, beta-phase soap formation is also inhibited by the addition of free fatty acid superfatting agents in levels above about 1%-2%. For all these reasons, therefore, it has not been possible hitherto to achieve significant improvements in the lathering characteristics of beta-phase soaps.
It has now been discovered that the addition of defined polymer materials to beta-phase soap bars has a beneficial effect on bar lathering (volume/richness) characteristics, both in soft and hard water conditions and than unexpectedly, the lathering improvement is achieved without detriment to beta-phase soap formation and without impairing transparency or translucency. The skin-feel and mildness characteristics of the bar are also significantly enhanced by use of the additives.